9.081 Lecture 6 Notes

Agenda I. Principles of Encoding II. MTL and Declarative Memory – Conscious/Explicit Memory? – Functional Distinctions within MTL? – MTL and Consolidation? Principles of Episodic Encoding Distribution of Practice Understanding Distributed Practice Stimulus Sampling Theory & Lag Effects Agenda I. Principles of Encoding II. MTL and Declarative Memory – Conscious/Explicit Memory? PFC, MTL, and Episodic Encoding Hippocampus & Memory Formation Hippocampus & Recollection What is the nature of MTL-mediated memory? • trace conditioning – may depend on MTL because acquisition of the CS–US association may require knowledge of the relationship to build and to be consciously remembered across many trials Agenda I. Principles of Encoding II. MTL and Declarative Memory – Conscious/Explicit Memory? – Functional Distinctions within MTL? MTL Memory System MTL Circuitry MTL Lesions and Amnesia H.M. and New Semantic Learning H.M. and New Semantic Learning H.M. and New Semantic Learning H.M. and New Semantic Learning Hippocampal Lesion & Semantic Learning? (Vargha-Khadem et al., 1997) • 3 patients with early, selective hippocampal insult • anterograde amnesia for everyday, episodic events • relative sparing of semantic learning abilities – – fared okay in mainstream education competent in speech & language • learned to read, write, & spell at levels commensurate with Verbal IQ • in normal range on vocabulary, information, & comprehension subtests of the VIQ scale • ability to comprehend and express ideas through language • thus, acquired requisite symbolic, semantic knowledge • relatively intact recognition including associative recognition within domain (e.g., word-word, face-face) impaired associative recognition across domains (e.g., voice-face, object-place) – intact familiarity-based item recognition, but impaired recollection Functional Segregation within MTL? Multiple MTL learning circuits (Aggleton & Brown, 1999) Agenda I. Principles of Encoding – – II. MTL and Declarative Memory – Conscious/Explicit Memory? – Functional Distinctions within MTL? – MTL and Consolidation? Retrograde Amnesia – Consolidation Retrograde Amnesia Retrograde Amnesia Retrograde Amnesia Modal Theory: MTL & Consolidation Modal Theory: MTL & Consolidation Modal Theory: MTL & Consolidation Flat Temporal Gradient in RA? Memory for Episodic Details Tests of declarative knowledge tend to be insensitive to level of episodic retrieval (Nadel et al., 2000) • 1–3 pt scoring based on retrieval of 3 = time and place, and some details of event 2 = less detail or time/place not specified 1 = only general info is provided • subjective & doesn’t discriminate between very rich episodic detail and those details that are just enough to warrant a full score • new scoring technique: just count the number of details provided Retrograde Amnesia: No Gradient for Episodic Details Multiple Memory Trace (MMT) Theory Traditional theory (Squire, 1992; McClelland et al., 1995) MTL provides a mechanism for linking together physically separated neocortical fragments (e.g., different types of event content) • • episodic and semantic memory have equivalent neural underpinnings, and thus should have similar temporal gradients (not always so) • stabilization of neocortical representations over time render MTL contributions unnecessary MMT theory (Nadel & Moscovitch, 1997) MTL is always involved in storage and retrieval of episodic memories, independent of age • • each episodic event is represented by a MTL memory trace, and traces replicate over time • long-term interactions between MTL and neocortex stabilize semantic memories over time (consolidation for semantic memory) MTT: MTL & Episodic Memory